Update: 2011-08-25 – Be sure you read the comments. Additional recent fixes have been added by others.
Update: 2010-07-23 – The new SL 2.1 viewer is causing people problems. It is an old error coming up again. There are several threads popping up on the SL forums. See: (Second Life WebKit Fail / Error – Problem Again) – One new solution is from Jesica (see comments), which is to find slplugin in the SL install folder, right-click for properties, and set it to Win95 compatibility mode.
Update: 2010-06-17 – With the release of Emerald Viewer version 2165 several people are running into this or a similar issue again. Those not having a problem installed to a new directory/folder rather installing over the top of the previous install. Others have copied the WebKit files from Snowglobe to fix the problem. Others just added slplugin to there anti-virus/firewall white list. In my version 2100 MOAP (Media On A Prim) isn’t working otherwise the viewer is fine. More to follow once I upgrade my viewer, watch for a 2165 review update.
A new problem with the Second Life 2.0 Beta Viewer and viewers based on the new viewer software. People are getting a popup error when starting the viewers. Some think it is the firewall, doesn’t seem to be. Somethink it is the anti-virus software, doesn’t seem to be. But, I have yet to find a solution.
JIRA VWR-17139 – Windows 7 With flash installed via mozilla auto discovery plugin fails to register in SL’s llMediaPlugin – Possible Solution for Windows 7 – The install of Adobe’s Flash 10 did not resolve the error for me.
Snowglobe users ran into this problem in October 2009… Its back…
The recent viewer update did not resolve the problem…
I added slplugin.exe to my Windows Firewall and told my anti-virus it is an exception. I checked my computer for older versions of slplugin.exe and replaced all the older versions with a copy of the latest. I rebooted the computer after the changes. After the restart the SL2.0 Beta viewer started without the error.
For now that appears to be the solution.